Various types of medium roll support devices of have been devised for conventional printers to accommodate different types or sizes of printing medium rolls to be mounted thereon in the conventional printers. A typical conventional printer has a first and second roll support holders respectively positioned at opposite ends of a compartment inside the conventional printer. For example, the U.S. Patent "Printing Media Roll Mounting and Positioning Mechanism" (U.S. Pat. No. 5,813,343) discloses such an arrangement of the first and second roll support holders respectively coupled to a support frame of the conventional printer defining the compartment inside the conventional printer. A conventional printing medium roll often includes a continuous printing medium strip wound on a cylindric tubular core. Correspondingly, the first roll support holder often has a support head adapted to receive and support the printing medium roll by inserting a first end of the tubular core onto a stair-like stepped extrusion on the support head of the first roll support holder. Similarly, the second roll support holder also has a support head adapted to receive and support a second end, opposite to the first, of the tubular core onto a stair-like stepped extrusion on the support head of the second roll support holder. The first and second roll support holders are vertically coupled to the printer having their respective support heads positioned at the top. Thus, the printing medium roll will be horizontally overhung inside the compartment of the printer by being supported by the first and second roll support holders at both ends.
Ordinarily, the first and second roll support holders of the conventional printer are coupled to each other through a connecting mechanism. The connecting mechanism includes a pair of substantially parallel first and second toothed racks respectively coupled to the first and second roll support holders at their respective bottom ends. The first and second toothed racks are spaced apart with each other in parallel and are further coupled to each other through a pinion positioned therein between. Teeth of the first and second toothed racks are respectively located at one side of the first and second toothed racks and are facing each other after the first and second toothed racks are coupled to the first and second roll support holders respectively. Moreover, teeth of the pinion mesh with teeth of the first and second toothed racks at diametrically opposite ends of the pinion, whereby the pinion will direct the first and second roll support holders to move toward each other at a first rotational direction and will direct the first and second roll support holders to move apart from each other at a second rotational direction, opposite to the first. The rotation of the pinion may be controlled manually by urging either the first or the second roll support holders inward or outward so as to pull them toward or away from each other respectively. When the first roll support holder is urged inward toward the second roll support holder, the first toothed rack will urge the pinion to rotate at the first rotational direction. Since the teeth of the pinion are meshing with the teeth of the second toothed rack at the diametrically opposite end, the pinion will move the second roll support holder inward through the rotation of the pinion at the first rotational direction. Conversely, when the first roll support holder is urged outward away from the second roll support holder, the pinion will be forced to rotate at the second rotational direction, opposite to the first, thereby urging the second roll support holder to move outward away from the first roll support holder. In addition, the pinion is positioned at approximately the center between the first and second roll support holders after mounted. As a consequence, through the above-mentioned arrangement of the connecting mechanism, the conventional printer could substantially center-justify the printing medium roll that is mounted on the first and second roll support holders with respectto a center line defined by the first and second roll support holders. Alternatively, the rotation of the pinion may be manually controlled by a rotating mechanism coupled to the pinion for directing the pinion to rotate in any desirable rotational direction, or it may be automatically controlled by a drive motor coupled to the conventional printer.
The pinion of the connecting mechanism of the conventional printer is often coupled to the support frame at a bottom side through a spindle. The spindle is positioned at approximately a center point on the support frame between the first and second roll support holders. The pinion has a center hole adapted to allow the spindle to thread through therein, thereby the pinion could rotate freely at opposite rotational directions about the spindle. The conventional printer may also include a spring coupled to one of the toothed racks and to the support frame, as shown in the '343 patent. The spring is designed to cause the first and second roll support holders to have the tendency to move toward each other so that the first and second roll support holders may hold the mounted printing medium roll firmly in between.
Although the conventional printer provides a mounting and positioning mechanism for printing media, many unresolved drawbacks remain to be overcome by further improvements. Specifically, incorporating the first and second roll support holders inside the printer would inevitably increase the lateral and/or vertical dimensions of the printer.
Furthermore, since the support heads of the first and second roll support holders respectively often includes a multiple-step extrusion, this design will further increase the lateral dimension of the conventional printer. As a result, it's particularly disadvantageous for a small portable printer to incorporate both the first and second roll support holders. In addition, having a complex medium roll support device as disclosed above, including the first and second support holders and the connecting mechanism therein between, will also increase the manufacturing costs of the conventional printer. This cost increase is very undesirable in this highly competitive market.